James Madison

"It will not be denied that power is of an encroaching nature and that  it ought to be effectually restrained from passing the limits assigned to it. After discriminating, therefore, in theory, the several classes of power, as they may in their nature be legislative, executive, or judiciary, the next and most difficult task is to provide some practical security for each, against the invasion of the others."

--James Madison, Federalist No. 48

Via Patriot Post